Inspecting apparatus of mounting state of component or printing state of cream solder in mounting line of electronic component

ABSTRACT

An inspecting apparatus is arranged on an electronic component mounting line for inspecting whether a mounting state of the component mounted by a mounting apparatus in a precedent process or a printing state of a cream solder by a cream solder printing apparatus in a precedent process is non-defective or defective. The inspecting apparatus includes an input device for taking data of the mounting state of the component to be inspected or the printing state of the cream solder to be inspected, a comparing device for comparing the data of the mounting state or the printing state input through the input device with an absolute decision criterion having a predetermined allowable range to decide whether the mounting state or the printing state is non-defective or defective and an operating state criterion which is within and narrower than the allowable range of the absolute decision criterion and a deciding device for deciding an operating state of the mounting apparatus or the cream solder printing apparatus in the precedent process based the data which is both within the absolute decision criterion and outside the operating state criterion.

BACKGROUND OF THE INVENTION

The present invention relates to an inspecting apparatus for inspectingthe mounting state of an electronic component or the printing state of acream solder on an electronic component mounting line.

With the recent trend toward mounting of small electronic componentchips on a printed circuit board, it has become difficult to visuallyinspect the mounting state of the electronic component or the printingstate of a cream solder of the electronic component by relying on thenaked eye of an operator. Accordingly, as depicted below, a inspectingapparatus is used for inspecting the printing state of cream solder.

In a conventional system shown in FIG. 19, the mounting state of eachprinted circuit board 2 supplied from a precedent process (a printingapparatus of a cream solder) 1 is inspected by an inspecting apparatus3. Non-defective ones and defective ones are respectively sent to asubsequent process 4 and a printed circuit board stockroom 5.

The inspecting apparatus 3 measures the area of the cream solder, etc.(mounting position, etc. in the case where the precedent process is amounting apparatus of an electronic component), thereby deciding, asshown in FIG. 6, that those in the allowable range are good ornon-defective (represented by (g)) and those outside the allowable rangeare not acceptable (indicated by (b)), on the basis of a preset absolutedecision criterion (A).

In the above example, however, since the decision of the inspectingapparatus 3 is based only on the absolute decision criterion (A), it isdifficult to know the operating state of the apparatus in the precedentprocess and to predict a dangerous state.

People skilled in the technical field may be able to devise aninspecting method of enabling the detection and monitoring of theoperating state of the apparatus in the preceding process 1 on the basisof all the data measured by the inspecting apparatus 3. However, in suchmethod it takes a long time to process all the data, therefore themethod suffers a drawback in that the dangerous condition cannot berapidly predicted based on data obtained in the precedent process in amass production system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an inspecting apparatusand method for inspecting a mounting state of an electronic component ora printing state of a cream solder on an electronic component mountingline which takes a shorter time to process all the data, thereforeproviding an advantage in that data used to predict a dangerouscondition can be obtained in the precedent process with rapid timing ina mass production system.

In accomplishing these and other objects, according to a first aspect ofthe present invention, there is provided an inspecting apparatusarranged on a mounting line of an electronic component for inspectingwhether or not a mounting state of the component mounted by a mountingapparatus in a precedent process or a printing state of a cream solderby a cream solder printing apparatus in a precedent process isnon-defective or defective, the inspecting apparatus comprising: aninput device for taking data of the mounting state of the component tobe inspected or the printing state of the cream solder to be inspected;a comparing means for comparing the data of the mounting state or theprinting state input through the input device with an absolute decisioncriterion having a predetermined allowable range to decide whether ornot the mounting state or the printing state is non-defective ordefective and an operating state criterion inside the allowable range ofthe absolute decision criterion and narrower than the allowable range;and a deciding means for deciding an operating state of the mountingapparatus or the cream solder printing apparatus in the precedentprocess when the data within the absolute decision criterion but outsidethe operating state criterion is input thereto subsequent to thecomparison.

According to the first aspect of the present invention, the inspectingapparatus is equipped with the operating state criterion, in addition tothe absolute decision criterion, to detect the operating state of theapparatus in the precedent process. The operating state of the apparatusin the precedent process is detected based on the inspecting data beyondthe operating state criterion (outside the allowable range).

Therefore, if the frequency of the inspecting data outside the operatingstate criterion is not smaller than a predetermined value, the operatingstate of the apparatus in the precedent process is decided to be notgood. Moreover, the operating accuracy of the apparatus in the precedentprocess can be detected specifically on the basis of the aboveinspecting data, so that the data predicting the dangerous condition canbe obtained for the apparatuses in the whole line.

Since it is so adapted that the data for predicting the dangerouscondition is not obtained by processing all the inspecting data, but byprocessing only the inspecting data outside the operating statecriterion, the present invention realizes the processing and decisionmaking of the data in a short time.

According to a second aspect of the present invention, there is providedthe inspecting apparatus in which the inspecting apparatus is aninspecting apparatus to decide whether or not the printing state of thecream solder is non-defective or defective by measuring an area of thecream solder on a printed circuit board printed by the cream solderprinting apparatus in the precedent process, the absolute decisioncriterion is formed on the basis of a design value of a metal mask todecide whether or not the printing state of the cream solder isnon-defective or defective, while the operating state criterion isformed on the basis of the design value of the metal mask to decidewhether or not the operating state of the cream solder printingapparatus is non-defective or defective, and the deciding means isprovided with: a deciding means for deciding whether or not there is adata within the absolute decision criterion, but outside the operatingstate criterion; an average value calculating means for calculating anaverage value of the data when the data is decided by the deciding meansto be outside the operating state criterion; a change deciding means fordeciding whether or not the calculated average value is shifted within apredetermined range; and an automatic criterion changing means forchanging the operating state criterion in such a manner as not to decidedefective as non-defective if the average value is decided by the changedeciding means to be shifted within the predetermined range, and theninputting a new operating state criterion to the comparison means toreplace the operating state criterion.

The second aspect of the present invention is provided to satisfy thefollowing demand other than the above-described objects if the aboveoperating state criterion is set on the basis of only the design valueof the metal mask. In other words, an error between the area of aspecified portion such as an opening portion of the metal mask and thedesign value thereof cannot be avoided as a result of the processingerror at the manufacturing time of the metal mask. A large error isoften generated particularly at a specific opening portion, for example.In some cases, the cream solder is actually correctly printed even whenthe area of the cream solder corresponding to the specific openingportion is detected to be outside the operating state criterion, andvice versa in an extreme case. Additionally, if it happens that the areaof the cream solder corresponding to the specific opening portion isfrequently decided to be outside the criterion, the operator might beobliged to measure the area of the opening portion of the metal mask bymeans of an optical microscope or the like to make the cause clear,which considerably decreases the operating efficiency.

In the above case where only the area of the cream solder correspondingto the specific opening portion exceeds the criterion so often, it maybe predicted to result from the processing error between the area of theopening portion and the design value. Therefore, if the criterion forthe specific opening portion is based on the design value of the metalmask, the actual state cannot be detected correctly.

In such a case as above, according to the second aspect of the presentinvention, the operating state criterion is automatically changed basedon the measuring data of the area of the cream solder to meet actualconditions.

According to a third aspect of the present invention, there is providedan inspecting apparatus for inspecting whether or not cream solders on aprinted circuit board printed by a cream solder printing apparatus arenon-defective or defective, the inspecting apparatus comprising: aprinting position detecting means for detecting printing positions ofthe cream solders printed at least at three points on the printedcircuit board, to thereby obtain a shifting amount of printing tocorrect a position of a metal mask or the printed circuit board; and anoutput means for outputting the shifting amount of printing to anautomatic position setting means for setting the position of the metalmask or the printed circuit board based on the shifting amount.

A printing position detecting means of an inspecting apparatus accordingto the third aspect of the present invention detects the printingposition of the cream solder printed at least at three points on theprinted circuit board, to thereby properly obtain the shifting amount ofthe printing position of the cream solder. The data of the shiftingamount is outputted to the printing apparatus, and the position of themetal mask is automatically corrected by an automatic position settingmeans of the printing apparatus. Accordingly, the cream solder can bealways printed with stable positioning accuracy and efficiently withoutbothering the operator for the correcting operation.

According to a fourth aspect of the present invention, there is providedan inspecting method for inspecting printing states of cream soldersprinted on a printed circuit board through a color image processing withthe use of an image picked up by an image pick-up device, whichcomprises: a setting process to set a window for a region in a picked-upimage where each cream solder is to be printed; a detecting process toperform color extraction of each cream solder within the window and thento detect patterns of the cream solders of areas not smaller than apreset value; a calculating process to calculate positions of the creamsolders from a sum of positions of centers of gravity of the detectedcream solder patterns corresponding to an area ratio of each detectedcream solder pattern; and a deciding process to decide whether or notthe printing states of the cream solders are non-defective or defectiveby comparing the calculated position with a reference position of eachcream solder.

The fourth aspect of the present invention is provided to satisfy thefollowing demand other than the above-described objects. Printing of acream solder has conventionally been inspected in a manner as describedbelow. As shown in FIG. 20(a), a window 69 is set in picked-up colorimage by an image pick-up device to surround the contour of a creamsolder 67. Then, as shown in FIG. 20(b), the color extraction of thecream solder 67 in the window 69 is carried out, and the area and theposition of the cream solder 67 are detected as one pattern (binarypattern after the color extraction and the detection). The cream solder67 is decided through comparison of the detected area with a referencearea and the detected position with a reference position. However, asillustrated in FIG. 21(a), a cream solder 77 formed on an electrodecomponent 78 of the printed circuit board may be partly dimmed andseparated to 77c and 77d depending on the printing state. In this case,each of the cream solders 77c and 77d in a window 79 is processedthrough color extraction, and then the areas and the positions of theextracted cream solders 77a, 77b are respectively detected as onepattern. In comparison between each detected area and a reference areaand between each detected position and a reference position, it isdecided whether or not the cream solder is printed properly. As aresult, even a good cream solder is decided to be a failure in the priorart.

Contrarily, in the inspecting method of the fourth aspect of the presentinvention, it becomes possible to correctly detect the position and thearea of a cream solder even if the cream solder is partly dimmed andseparated from one another depending on the printing condition.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1A is a schematic block diagram of a mounting line including aninspecting apparatus according to a first embodiment of the presentinvention;

FIG. 1B is a block diagram of the inspecting apparatus of FIG. 1A;

FIG. 2 is a diagram showing the inspecting criterion of the inspectingapparatus of FIG. 1A;

FIG. 3A is a diagram showing the whole of a cream solder printingapparatus with an inspecting apparatus according to a second embodimentof the present invention;

FIG. 3B is a schematic block diagram of a mounting line including theinspecting apparatus according to the second embodiment of the presentinvention;

FIG. 3C is a block diagram of the inspecting apparatus of FIG. 3B;

FIG. 3D is a flow chart of the operation of the inspecting apparatus ofFIG. 3C;

FIG. 4 is a graph of the distribution model of the area of cream solder;

FIG. 5 is a schematic block diagram of a mounting line including aninspecting apparatus;

FIG. 6 is a graph showing an absolute decision criterion;

FIG. 7 is a schematic block diagram of a mounting line including aninspecting apparatus according to a third embodiment of the presentinvention;

FIG. 8 is a diagram showing the inspecting criterion of the inspectingapparatus of FIG. 7;

FIG. 9 is a plan view of a printed circuit board in a modified exampleof the third embodiment;

FIG. 10 is a diagram showing the inspecting criterion of an inspectingapparatus according to a further modification of the third embodiment;

FIG. 11 is a schematic diagram of a driving mechanism of a metal mask inthe modification of FIG. 10;

FIG. 12 is a schematic diagram of a driving mechanism of a printedcircuit board in the modification of FIG. 10;

FIG. 13 is a partial view of the driving mechanism of the printedcircuit board in FIG. 12;

FIG. 14 is a schematic block diagram of an apparatus to be used in aninspecting method of printing of cream solder according to a fourthembodiment of the present invention;

FIG. 15 is a flow chart of the inspecting method according to the fourthembodiment of the present invention;

FIG. 16 is a flow chart of an inspecting method according to a modifiedexample of the fourth embodiment;

FIGS. 17(a), 17(b), and 17(c) are respectively schematic diagrams of aprinted pattern of cream solder corresponding to the inspecting methodof FIG. 15;

FIGS. 18(a), 18(b), 18(c), and 18(d) are respectively schematic diagramsof a printed pattern of cream solder corresponding to the inspectingmethod of FIG. 6;

FIG. 19 is a schematic block diagram of a mounting line including aconventional inspecting apparatus;

FIGS. 20(a) and 20(b) are respectively schematic diagrams of a printedpattern of cream solder in a conventional inspecting method when part ofthe cream solder is dimmed, but not separated; and

FIGS. 21(a) and 21(b) are respectively schematic diagrams of a printedpattern of cream solder in a conventional inspecting method when part ofthe cream solder is dimmed and separated from each other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

A first embodiment of the present invention will be described withreference to FIGS. 1A, 1B, and 2.

In FIG. 1A, a mounting apparatus 6 for mounting electronic components onworks in a precedent process, an inspecting apparatus 7 for inspectingthe mounting state of processed works in the precedent process and amounting apparatus 8 for mounting electronic components on works in asucceeding process are all arranged on the mounting line. A printedcircuit board (work) 9 processed by the apparatus 6 in the precedentprocess is inspected by the inspecting apparatus 7. If electroniccomponents are properly mounted on the work, the work is transferred tothe apparatus 8 for the succeeding process. An inferior work (defective)is sent to, for example, a printed circuit board stockroom.

An absolute decision criterion (A) is set for the apparatus 7, as shownin FIG. 2. The apparatus 7 decides whether or not the mounting state ofelectronic components on the work is good within the predeterminedallowable range of the criterion (A). At the same time, an operatingstate criterion (L) which is narrower in the range than the absolutedecision criterion (A) within the absolute decision criterion (A) isalso set for the apparatus 7.

The above inspecting apparatus 7 is provided with a measuring device 7awhich measures the mounting area and position of the each of electroniccomponents in an electronic component mounting apparatus, or measuresthe area and position of a cream solder at an optional point on theprinted circuit board, a comparison means 7b for comparing each data ofthe area and position measured by the measuring device 7a with thecorresponding absolute decision criterion (A) and the operating statecriterion (L), a memory means 7c for storing the comparing result, andan output means 7d for outputting a predetermined data stored in thememory means 7c to a decision means 10 for deciding the operating statein the precedent process. A concrete example of the measuring device 7ais shown in FIG. 14.

Referring to FIG. 2, in the case, for example, where the apparatus 6 isa cream solder printing apparatus and an object to be inspected is thearea of the cream solder, the absolute decision criterion (A) is set inthe range of from S1 to S4, and the operating state criterion (L) is setin the range of from S2 to S3 (S1<S2<S3<S4 . . . area of the creamsolder). The to-be-inspected object may possibly be the positional shiftof the cream solder.

The inspecting apparatus 7 determines the object to be good(non-defective) if the object is within the allowable range (indicatedby (g1), (g2) in FIG. 2) and defective if the object is outside theallowable range (denoted by (b)) based on the absolute decisioncriterion (A). The good work is sent to the apparatus 8 for thesucceeding process, while the defective one is transferred to a printedcircuit board stockroom or the like.

The inspecting apparatus 7 is additionally provided with the decisionmeans 10 for deciding the operating state of the apparatus 6 in theprecedent process on the basis of the inspecting data outside theoperating state criterion (L) and inside the allowable range of theabsolute decision criterion (A) (corresponding to those represented by(g2) in FIG. 2). Accordingly, only the inspecting data represented by(g2) is stored and retained (shown by (p) in FIG. 1A), based on whichthe operating state of the apparatus 6 is detected. For instance, if theinspecting data represented by (g2) is generated at a higher frequencythan a predetermined value, a danger predicting data (indicated by (q)in FIG. 1A) is fed to the apparatus 6 to provide an indicating that theoperating state of the apparatus 6 must be inspected and corrected,thereby avoiding production of inferior works. Moreover, the inspectingdata indicated by (g2) is made use of detecting how the operating stateof the apparatus 6 is (e.g., whether the cream solder is blurred ordimmed) or how the accuracy is, to thereby perform an appropriatetreatment.

Since the decision means 10 handles only the inspecting data indicatedby (g2), the decision means 10 is able to make a decision in a shorttime. Even if the apparatus 6 should be stopped in an emergency inaccordance with the danger predicting data (q), it will be carried outwith respect to a mass production system.

Although the decision means 10 handles only the inspecting dataindicated by (g2) in the above first embodiment, it can be so designedthat the inspecting data represented by (b) is also treated by thedecision means 10. In addition, although the operating state criterion(L) is a single criterion set in the above embodiment, a plurality ofoperating state criteria (L) may be prepared for the inspectingapparatus 7.

The inspecting apparatus in the first embodiment of the presentinvention as above is capable of distinguishing not only proper andimproper works, but the operating state of the apparatus in theprecedent process reliably and quickly.

A second embodiment of the present invention will be depicted below withreference to FIGS. 3A-6.

FIG. 3A illustrates the whole of a cream solder printing apparatus 11.In FIG. 3A, reference numerals respectively represent: 71 a recognizingdevice such as a camera or the like for recognizing the printing mark ona printed circuit board 9; 72 a main body of the printing apparatus 11;73, 78 guide rails for guiding the printed circuit board 9; 74 a drivingdevice of a table supporting the printed circuit board 9 at the printingtime; 75 a metal mask; and 76 a transfer device for transferring theprinted circuit board 9 to a predetermined position. The printed circuitboard 9 is set at a position 77 of the transfer device 76. In the creamsolder printing apparatus, when the mark on the printed circuit board 9is recognized by the recognizing device 71, the printed circuit board 9is transferred to the printing position from the guide rail 78 by thetransfer device 76 and set on the table. Subsequently, the printedcircuit board is printed in a predetermined manner by the cream soldervia the metal mask 75 by the main body 72. The printed circuit board 9after printing is discharged from the printing apparatus by the otherguide rail 73.

An inspecting apparatus 13 which inspects the printing state of thecream solder on the printed circuit board 9 by measuring the area of thecream solder printed by the cream solder printing apparatus 11 in theprecedent process is the same as the inspecting apparatus 7 discussedafterward with reference to FIG. 15. As in FIG. 2, the inspectingapparatus 13 is provided with an absolute decision criterion (A) formedon the basis of each design value of the metal mask so as to detect theprinting state of the cream solder, and an operating state criterion (L)formed on the basis of each design value of the metal mask so as todetect the operating state of the cream solder printing apparatus 11.

Concretely, as shown in FIGS. 3B and 3C, a criterion changing means isadded to the inspecting apparatus 13, more specifically, to thecomparing means 7b of the inspecting apparatus 7 in the firstembodiment. In other words, the inspecting apparatus 13 is provided witha measuring device 7a, a comparison means 7b, a decision means 13a, anaverage calculating means 13b, a change deciding means 13c, and anautomatic criterion changing means 13d. The measuring device 7a measuresthe area and position of the cream solder at an optional point (n) onthe printed circuit board 9. The comparison means 7b forms and storeseach absolute decision criterion (A) by adding the allowable value(indicated by percentage or an absolute value) fit for the efficiency ofthe line to each design value of the position and area of the metalmask, forms and stores each operating state criterion (L) within eachabsolute decision criterion (A), and compares the data of the area andposition measured by the measuring device 7a with the respectiveabsolute decision criteria (A) and the operating state criteria (L). Thedecision means 13a decides whether only the data of the area andposition at a specific section of the cream solder is within theabsolute decision criteria (A) and outside the operating state criteria(L). The average calculating means 13b calculates the respective averagevalue of the data of the specific section when the data of the specificsection is decided to be outside the operating state criteria (L) by thedecision means 13a. The change deciding means 13c decides whether or notthe respectively calculated average value is shifted within the range ofpreset values. The automatic criterion changing means 13d changes theoperating state criterion (L) to an operating state criterion (L') in amanner not to determine a defective work as good if the change decidingmeans 13c decides that the average value is shifted within the range ofpreset values, and inputs the new operating state criterion (L') to thecomparison means 7b to replace the operating state criterion (L) withthe operating state criterion (L').

The fundamental operation of the measuring device 7a and the comparisonmeans 7b in the inspecting apparatus 13 is the same as in the firstembodiment. Therefore, only a differences will be described hereinbelow.FIG. 3D is a flow chart of the operation when the data of the specificsection is decided to be outside the operating state criterion (L) bythe decision means 13a. The area and position of the cream solder at anoptional point (n) on the printed circuit board 9 are measured by themeasuring device 7a in step #10, and then, the average value of each ofthe area and position measured by the measuring device 7a is calculatedby the average calculating means 13b in step #11. In comparison betweeneach calculated average value and each design value of the metal mask,the change deciding means 13c decides in step #12 whether or not eachcalculated average value is shifted within each range of preset values.In the case where the average value is not shifted, the operating statecriterion (L) is not changed. If the average value is shifted, theoperating state criterion (L) is changed to (L') by the automaticcriterion changing means 13d in step #13 in a manner not to decide aninferior work to be good. The operating state criterion (L') is input tothe comparison means 7b, so that the operating state criterionafterwards becomes (L').

Using each design value (S₀) of the metal mask as the center, an upperlimit of the absolute decision criterion (A) is set to be (S4), while alower limit thereof is (S1). The works within the range of from (S4) to(S1) are decided to be good (indicated by (g1), (g2) in FIG. 2), andthose outside the range are decided to be defective (indicated by (b) inFIG. 2). The inspecting apparatus 13 sends the good ones to thesucceeding process and the defective ones to a printed circuit boardstockroom 15. The absolute decision criterion (A) is absolute and neverchanged at all in the middle of the process.

An upper limit and a lower limit of the operating state criterion (L)are initially set to be (S3) and (S2), respectively, while each designvalue (S₀) of the metal mask is at the center value located between theupper and lower limits. Within the range (S3-S2), the operating state inthe precedent process is determined to be normal. Outside the range,however, the operating state is decided to be abnormal. The range(S3-S2) is set within the range (S4-S1) of the absolute decisioncriterion (A).

If the area of the cream solder is frequently detected to be not smallerthan (S3), it is found by using the operating state criterion (L) thatthe cream solder is inclined to ooze, and therefore, the printingcondition of the printing apparatus 11 is corrected so that the creamsolder is turned to be printed faintly.

In the case where only the area of the cream solder corresponding to aspecific opening portion of a printed circuit board is decided to beoutside the operating state criterion (L) by the decision means 13a, aprocess error is presumed to be present between the area of the openingportion and each design value and then it is presumed to be an errorthat the center value of the operating state criterion (L) is set to be(S₀). In such case as above, as shown in FIGS. 3B and 3C according tothe second embodiment, many measuring results of the area of the creamsolder corresponding to the specific opening portion are collected andstored, and then an average value thereof (S₀ ') is calculated by theaverage calculating means 13b so as to change the center value (S₀).Then, each of the calculated average values (S₀ ') of the area andposition is compared with each of the design values of the metal mask bythe change deciding means 13c, thereby to decide whether or not each ofthe calculated average values is shifted within the range of presetvalues. The operating state criterion (L) is not changed if thecalculated average value has no shift. If the average value is shifted,the operating state criterion (L) is changed by the automatic criterionchanging means 13d to the operating state criterion (L') which has theaverage value (S₀ ') as the center value so that an inferior product isnot decided to be good. The operating state criterion (L') is input tothe comparison means 7b and used afterwards.

In FIG. 4, (P) indicates the distribution model of the area of the creamsolder in the case where the opening portion is designed in compliancewith each design value of the metal mask and, (Q) is the distributionmodel of the area of the cream solder when a process error is present inthe opening portion of the metal mask. The automatic criterion changingmeans 13d makes it possible to decide the printing state of the creamsolder based on the actually measured area of the opening portion of themetal mask while using the operating state criterion (L') having thecenter value (S₀ '), the upper limit (S3'), and the lower limit (S2').

In the second embodiment, the automatic criterion changing means 13d isso adapted as to change the criterion (L) to (L') only when the openingportion is outside the operating state criterion (L). However, theoperating state criterion (L) may be made changeable to any openingportion whether the opening portion is inside or outside the criterion(L).

According to the second embodiment, the inspecting apparatus can decidenot only whether the printing state of the cream solder is good or bad,but the operating state of the printing apparatus accurately withoutbeing influenced by the process error of the metal mask. The workingcondition is thus made proper.

A third embodiment of the present invention will now be described withreference to FIGS. 7-13.

In FIG. 7, a cream solder printing apparatus 11 in the precedentprocess, an inspecting apparatus 13 for the inspection of printing ofthe cream solder, and an apparatus 8 for the succeeding process arealigned on the mounting line. The printing state of the cream solder ofa printed circuit board 9 printed by the printing apparatus 11 isinspected by the inspecting apparatus 13. A good printed circuit boardis forwarded to the succeeding apparatus 8, while a defective printedcircuit board is sent to the printed circuit board stockroom 15.

As shown in FIG. 2, the inspecting apparatus 13 has an absolute decisioncriterion (A) of a predetermined allowable range so as to decide theprinting state of the cream solder. Based on the criterion (A), theinspecting apparatus 13 decides those within the allowable range to begood (indicated by (g)) and those outside the range to be inferior(indicated by (b)), and sends good ones to the succeeding process andinferior ones to the printed circuit board stockroom 15.

The inspecting apparatus 13 is provided with a printing positiondetecting means 31 for detecting the printing position of the creamsolder at least at three points on the printed circuit board 9 therebyto obtain the shifting amount of printing. The printing positiondetecting means 31 detects centers of cream solders Q1, Q2, and Q3printed on the electrode surfaces P1, P2, and P3 shown in FIG. 8. Thecenters of the electrode surfaces P1, P2, and P3 are known beforehandfrom the design values of the printed circuit board. The shifting amount(x) in the X direction and the shifting amount (y) in the Y directionbetween the center of the cream solder and the center of thecorresponding electrode surface are obtained at each of the above threepoints. The printing position detecting means 31 calculates the averagevalue of each of the shifting amounts (x) and (y) of three points. Theaverage values are sent as the data of the shifting amounts of printingto an automatic metal mask position setting means 33 of the printingapparatus 11 via a transmission means 32 such as a wire.

The automatic position setting means 33 is well known and set in thecream solder printing apparatus 11 to automatically determine theinitial setting position of the metal mask. The automatic setting means33 is utilized to automatically correct the position of the metal maskin the third embodiment.

Although the shifting amount of printing is detected at three points onthe printed circuit board in the above embodiment, it may be detected atfour or more points of the printed circuit board. Moreover, as isreadily understood from FIG. 9, the electrode surfaces P1, P2, and P3may be formed at three or more points at the corner of the printedcircuit board 9 and the shifting amount may be detected with the use ofthe cream solder printed on these electrode surfaces.

A modified example of the third embodiment will now be depictedhereinbelow, whereby the shifting amount of printing is detected at twopoints and the shifting amount of the rotating angle of a straight lineconnecting the two points is detected.

In FIG. 10, reference numerals respectively indicate: 9 a printedcircuit board to be inspected; 82 coordinates (X1,Y1) of the designvalue of a first shift correcting land; 83 coordinates (X2,Y2) of thedesign value of a second shift correcting land; 84 coordinates (x1,y1)of the center of the cream solder printed on the first shift correctingland; and 85 coordinates (x2,y2) of the center of the cream solderprinted on the second shift correcting land.

The shifting amounts (x,y,θ) in the X, Y, θ (rotation) directions areexpressed by equations as follows:

    x=|(X1+X2)/2-(X1+X2)/2|

    Y=|(Y1+Y2)/2-(Y1+Y2)/2|

    θ=tan.sup.-1 {(Y2-Y1)/(X2-X1)}-tan.sup.-1 {(y2-y1)/(x2-x1)}

It is to be noted here that either of tan⁻¹ (*)=90° or tan⁻¹ (*)=tan⁻¹(*)+180° is held when the denominator is equal to zero.

Now, a mechanism to correct the detected shifting amount will bediscussed below.

Referring to FIG. 11, an X-axis driving device 91 is driven so as tomove a metal mask 94 in the X-axis direction. If the metal mask 94 is tobe driven in the Y-axis direction, two Y-axis driving devices 92, 93 aresynchronously driven. In order to rotate the metal mask 94 in the θdirection, the X-axis driving device 91 and one Y-axis driving device 93are activated while the other Y-axis driving device 92 is heldstationary, so that the printed circuit board 9 is rotated around (O). Arotary shaft of the motor of each driving device is provided with a ballscrew. Since a part of the metal mask 94 is fitted in the ball screwpart of the rotary shaft, the metal mask 94 coupled to the rotary shaftof the motor is moved to and fro along a predetermined direction inaccordance with the rotation of the motors in the forward and backwarddirections.

A table 101 supporting the printed circuit board 9 may be moved, insteadof moving the metal mask 94. As shown in FIG. 12, an X-axis drivingdevice 102 is actuated to move the table 101 in the X-axis direction. AY-axis driving device 103 is actuated to move the table 101 in theY-axis direction. Meanwhile, when the table 101 should be moved in the θdirection, as shown in FIG. 13, a projection 105a projecting in theradial direction from an annular part 105b secured to the bottom surfaceof the table 101 is fitted into a groove 104a of the rotary shaft of aθ-direction driving device 104, and the projection 105a together withthe groove 104a is linearly moved following the rotation of the rotaryshaft. As a result, the annular part 105b guided by a cylindrical guidemember 106 is rotated forward and backward to move in the θ direction.

According to the inspecting apparatus of the third embodiment of thepresent invention described above, not only the printing state of thecream solder on the printed circuit board can be detected, but thepositional shift of the metal mask is detected thereby to automaticallycorrect the position of the metal mask properly. Therefore, the creamsolder can be printed with stable positioning accuracy. At the sametime, the positional shift of the metal mask can be correctedefficiently.

A fourth embodiment of the present invention, namely, an inspectingmethod of printing of cream solder will be described hereinbelow withreference to FIGS. 14-18.

A flow chart of FIG. 15 of the fourth embodiment will be explained withreference to FIGS. 14 and 17. In FIGS. 14, 15, and 17, as thepretreatment, a reference value (Sk) of the area of the individual creamsolder and a position reference value (Xk,Yk) are input to an imagerecognizing device 54 and set in a memory. The reference value (Sk) iscalculated from each design value of a metal mask to show an area valueof individual patterns. The position reference value (Xk,Yk) iscalculated from each design value of a metal mask to show a centerposition of gravity of individual patterns. Moreover, an area (SL) to bedecided as a noise pattern, an allowable value (DX,DY) of the positionalshift when the cream solder is decided to be inferior, an allowablevalue (DS) of the area, an outer dimension (Wx,Wy) of the individualcream solder, and an allowable value of the window (Cw) are also inputto the device 54 to be set in the memory (step #21). The area (SL) to bedecided as a noise pattern is an area value equal to or more than apredetermined value set previously, that is, an area of the minimumindividual pattern of individual patterns of dirt or contaminant of aprinted circuit board, or dirt of a cream solder printed by a creamsolder printing method. In the allowable value (DX,DY) of the positionalshift, it is supposed that the maximum value of a positional shift inthe X direction is DX, and the maximum value of a positional shift inthe Y direction is DY. The allowable value (DS) of the area is anallowable value of an operating state criterion within an absolutedecision criterion which is found by adding an allowable value(percentage or absolute value) corresponding to a mounting line abilityto each allowable design value of an area of an individual pattern ofthe metal mask. The allowable value of the window (Cw) is the maximumvalue of positional shifts of the metal mask.

As in FIG. 14, an image pick-up unit 53 picks up an image of the printedcircuit board 9 on which a cream solder 52 is printed (step #22). Awindow 59 is set for a cream solder 57 of the picked-up color image, asis clear in FIG. 17(a). The window 59 is of the size obtained by addingthe allowable value (Cw) of the window to the outer dimension (Wx,Wy) ofeach of the individual cream solders 57. The center of the window 59corresponds to the positional reference value (Xk,Yk) of the creamsolder 57 (step #23). The color extraction of the cream solder 57 iscarried out through the color recognition inside the window 59, as shownin FIG. 17(b), and all the patterns of the cream solder (PC1, PC2, . . ., PCn) of the area not smaller than the preset value (SL) are detected(step #24). Then, the position of the cream solder is detected accordingto an expression (1) below from the sum of the position of the center ofgravity of each pattern corresponding to the area ratio of the detectedpatterns of the cream solder (step #25). ##EQU1##

The positional shift is decided according to a decision expression belowbased on the calculated position (X,Y), a preliminarily stored referenceposition (Xk,Yk), and an allowable value of the positional shift (DX,DY)(step #26).

Decision expression Xk>X+DX or Xk<X-DX

Otherwise, decision expression Yk>Y+DY or Yk<Y-DY

If any of the above expressions is satisfied, printing is decided to beNG (no good). If none of the above expressions is held, printing isdecided to be OK (step #26). Further, the area is decided according tothe following expression on the basis of the detected area (S), thepreliminarily set reference value (Sk), and the allowable value (DS)(step #27).

Sk>S+DS

or Sk<S-DS

If either expression is held, printing is decided to be NG. On the otherhand, when neither is held, printing is detected to be OK (step #27). Inthe case where NG is output in step #26 or #27, the cream solder isdecided to be inferior (#28).

Referring back to FIG. 14, 55 indicates a keyboard and 56 is a cathoderay tube (CRT) as a display device.

A modified example of the fourth embodiment will be described withreference to a flow chart in FIG. 16 and, FIGS. 14 and 18. In FIGS. 14,16, and 18, the reference value (Sk) of the area of the individual creamsolder 57 and the positional reference value (Xk,Yk) are input to theimage recognizing device 54 and set in the memory beforehand. At thesame time, the area (SL) to be detected as a noise pattern, theallowable value (DX,DY) of the positional shift to decide that the creamsolder is no good, the allowable value (DS) of the area, the outerdimension (Wx,Wy) of an individual electrode section (referred to as aland hereinafter) of the printed circuit board, and the allowable valueof the window (Cw) are input to the recognizing device 54 and set in thememory (step #31).

As shown in FIG. 14, the image pick-up unit 53 picks up the image of theprinted circuit board 9 having the cream solder 52 printed on a land 58(step #32). In FIG. 18(a), the window 59 is set for the land 58 of theobtained color image. The window 59 is of the outer size of theindividual land 58 and completely fits the configuration of the land 85(step #33). In FIGS. 18(b) and 18(c), the color extraction of the land58 is performed through the recognition of color in the window 59,thereby to detect all the binarized land patterns (PL1, PL2, . . . )(Step #34). In FIG. 18(d), the detected land patterns are subjected tothe black-and-white inversion, and accordingly, pseudo patterns (PC1,PC2, . . . , PCn) are detected (step #35). The pseudo patterns areindividual patterns except for individual patterns of the electrodes ofthe printed circuit board which are detected from the windows which arecircumscribed rectangles of the electrodes. The position of the creamsolder is detected by the equation (1) described earlier from the sum ofthe position of the center of gravity of each pseudo patterncorresponding to the area ratio of the detected pseudo patterns (step#36).

The positional shift is hence decided in accordance with the followingexpression from the detected position (X,Y) and the reference position(Xk,Yk) and allowable value of positional shift (DX,DY) eachpreliminarily set in the memory:

Xk>X+DX

or Xk<X-DK

or Yk>Y+DY

or Yk<Y-DY

If any one of the above expressions is held, printing is decided to beNG. On the contrary, printing is decided to be OK when none of theexpressions is satisfactorily supported (step #37).

Moreover, the area is decided according to the following expressionbased on the detected area (S), and the reference value (Sk) and theallowable value (DS) each stored in the memory:

SK>S+DS

or Sk<S-DS

When either one is satisfied, NG is decided. Otherwise, if bothexpressions are not held, printing is decided to be OK (step #38). Thecream solder is decided to be improperly printed in the case where NG isgenerated in step #37 or #38 (step #39).

The inspecting method in the fourth and modified embodiments of thepresent invention is effective to correctly detect the position and areaof the cream solder even if the cream solder is partly blurred andseparated from one another due to the printing condition.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

What is claimed is:
 1. An inspecting method for a mounting line forinspecting an assembly state of an article obtained from a precedentprocess in the mounting line, which comprises the steps of:using animage pick-up device to obtain an image of the article; generatingmeasurement data indicative of the assembly state of the article fromthe image obtained by the image pick-up device; comparing themeasurement data of the assembly state with an absolute decisioncriterion defining a predetermined allowable range of the measurementdata and comparing the measurement data with an operating statecriterion defining a second predetermined allowable range of themeasurement data which is within the and narrower than the firstpredetermined allowable range; and deciding whether the assembly stateof the article is defective based on whether the measurement data iswithin the first predetermined allowable image, and deciding anoperating state of the proceeding process of the mounting line based onmeasurement data which is within the first predetermined allowable rangeand outside the second predetermined allowable range; wherein theprecedent process is cream soldering by a cream soldering apparatus, andwherein the assembly state is a cream solder state of a printed circuitboard printed by the cream solder printing apparatus in the precedentprocess, wherein the absolute decision criterion and the operating statecriteria are in accordance with a design value of a metal mask used inthe cream soldering printing apparatus, wherein the deciding stepcomprises the steps of: identifying measurement data which is bothwithin the absolute decision criterion and outside the operating statecriterion; calculating an average value of the measurement dataidentified in the identifying step; deciding whether the calculatedaverage value is shifted within a predetermined range; and changing theoperating state criterion in a manner not to decide defective asnon-defective if the average value is decided in the change decidingstep to be shifted within the predetermined range, and then replacingthe operating state criterion with a new operating state criterion. 2.An inspecting apparatus arranged on an electronic component mountingline for inspecting an assembly state of an article obtained from aprecedent process of the mounting line, the inspecting apparatuscomprising:an image pick-up device for obtaining an image of thearticle; means for generating measurement data indicative of theassembly state of the article to be inspected from the image obtained bysaid image pick-up device; a comparing means for comparing themeasurement data of the assembly state with an absolute decisioncriterion defining a first predetermined allowable range of themeasurement data and for comparing the measurement data of the assemblystate with an operating state criterion defining a second predeterminedallowable range of the measurement data which is within and narrowerthan the first predetermined allowable range; and a deciding means fordeciding whether the assembly state of the article is defective based onwhether the measurement data is within the first predetermined allowablerange, and for deciding an operating state of the precedent process ofthe mounting line based on measurement data which is within the firstpredetermined allowable range and outside the second predeterminedallowable range; wherein the precedent process is cream soldering by acream soldering apparatus, and wherein the assembly state is a creamsolder state of a printed circuit board printed by the cream solderprinting apparatus in the precedent process, wherein the absolutedecision criterion and the operating state criteria are in accordancewith a design value of a metal mask used in the cream soldering printingapparatus, and wherein the deciding means includes: an identifying meansfor identifying data which is both within the absolute decisioncriterion and outside the operating state criterion; an average valuecalculating means for calculating an average value of measurement dataidentified by the identifying means; a change deciding means fordeciding whether the calculated average value is shifted within apredetermined range; and an automatic criterion changing means forchanging the operating state criterion in a manner not to decidedefective as non-defective if the average value is decided by the changedeciding means to be shifted within the predetermined range, and theninputting a new operating state criterion to the comparison means toreplace the operating state criterion.